1. Field of the Invention
The present invention relates to an audio signal processor, and more particularly, to a noise gate apparatus for an digital audio processor.
2. Background of the Related Art
As shown in FIG. 1, a related art digital audio processor includes an input unit 1, a gain control unit 2, a signal processor 3, a volume controller 4 and an output unit 5. The input unit 1 converts the type of data being input depending upon whether, for example, an internal data is operated based on 16 bits or on 32 bits. The gain controller 2 multiplies a first predetermined value to the converted data to control the size of an input data and prevent the input data from overflowing. The signal processor 3 processes an output signal from the gain control unit 2. The volume controller 4 multiplies a signal processed in the signal processor 3 by second predetermined value to control the size (e.g., volume) of an output signal, and the output unit 5 converts then outputs data appropriate to an external output data type.
As shown in FIG. 2, the signal processor 3 includes a buffer 31 for storing the output signal of the gain control unit 2 and an operator 32 for operating data stored in the buffer 31. The signal processor 3 further includes an operation coefficient unit 33 for determining an operation coefficient to be operated in the operator 32 and a controller 34 for controlling the buffer 31, the operator 32 and the operation coefficient unit 33.
The operation of the related an digital audio processor will now be described. In the input unit 1, an externally applied format data is converted to data that can be processed in an internal audio apparatus. For example, external data of a serial format can be converted to a parallel format data using an external synchronous signal. Accordingly, the data can be expanded and the resultant value is adjusted to a bit and width of data used in the internal audio apparatus.
The data converted in the input unit 1 is amplified by a first predetermined amount in the gain control unit 2 and applied to the signal processor 3. The data applied to the signal processor 3 is buffered in the buffer 31 and operated in the operator 32. The operated signal is then amplified by a second predetermined amount in the volume controller 4. The output signal from the volume controller 4 is converted to a prescribed type of external output data by the output unit 5 and then outputted.
However, the related art digital audio processor has various disadvantages. For example, when the values outputted respectively from the gain control unit 2 and the volume controller 4 are too small, a frequency component different from the input signal is output as shown in FIG. 3B compared to the input signal shown in FIG. 3A, thereby generating noise.